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MATLAB is a numeric computation software for engineering and scientific calculations. The name MATLAB

stands for MATRIX LABORATORY. MATLAB is primarily a tool for matrix computations. It was developed by

John Little and Cleve Moler of MathWorks, Inc. MATLAB was originally written to provide easy access to the

matrix computation software packages LINPACK and EISPACK.

MATLAB is a high-level language whose basic data type is a matrix that does not require dimensioning. There is

no compilation and linking as is done in high-level languages, such as C or FORTRAN. Computer solutions in

MATLAB seem to be much quicker than those of a high-level language such as C or FORTRAN. All computations

are performed in complex-valued double precision arithmetic to guarantee high accuracy.

MATLAB has a rich set of plotting capabilities. The graphics are integrated in MATLAB. Since MATLAB is also

a programming environment, a user can extend the functional capabilities of MATLAB by writing new modules.

MATLAB has a large collection of toolboxes in a variety of domains. Some examples of MATLAB toolboxes are

control system, signal processing, neural network, image processing, and system identification. The toolboxes

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When MATLAB is invoked, the command window will display the prompt >>. MATLAB is then ready for entering

data or executing commands. To quit MATLAB, type the command

exit or quit

MATLAB has on-line help. To see the list of MATLAB’s help facility, type

help

The help command followed by a function name is used to obtain information

on a specific MATLAB function. For example, to obtain information on

the use of fast Fourier transform function,

fft, one can type the command

help fft

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The basic data object in MATLAB is a rectangular numerical matrix with real or complex elements. Scalars are thought of as

a 1-by-1 matrix. Vectors are considered as matrices with a row or column. MATLAB has no dimension statement or type

declarations. Storage of data and variables is allocated automatically once the data and variables are used.

MATLAB statements are normally of the form:

variable = expression

Expressions typed by the user are interpreted and immediately evaluated by the MATLAB system. If a MATLAB statement

ends with a semicolon, MATLAB evaluates the statement but suppresses the display of the results. MATLAB is also capable

of executing a number of commands that are stored in a file. This will be discussed in Section 1.6. A matrix

may be entered as follows:

A = [1 2 3; 2 3 4; 3 4 5];

=

5

4

3

4

3

2

3

2

1

A

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Note that the matrix entries must be surrounded by brackets [

] with row elements separated by blanks or

by commas. The end of each row, with the exception of the last row, is indicated by a semicolon. A matrix A can also

be entered across three input lines as

A = [ 1 2 3

2 3 4

3 4 5];

In this case, the carriage returns replace the semicolons. A row vector B with four elements

B = [ 6 9 12 15 18 ]

can be entered in MATLAB as

B = [6 9 12 15 18];

or

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MATLAB is case sensitive in naming variables, commands and functions. Thus b and B are not the same variable. If

you do not want MATLAB to be case sensitive, you can use the command

casesen off

To obtain the size of a specific variable, type

size ( ). For example, to find the size of matrix A, you can execute the

following command:

size(A)

The result will be a row vector with two entries. The first is the number of rows in A, the second the number of

columns in A.

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To find the list of variables that have been used in a MATLAB session, type the command

whos

There will be a display of variable names and dimensions. Table 1.1 shows the display of the variables that have

been used so far in this lesson:

Table 1.1

Display of an output of whos command

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Table 1.2 shows additional MATLAB commands to get one started on MATLAB. Detailed descriptions and

usages of the commands can be obtained from the MATLAB help facility or from MATLAB manuals.

Table 1.2

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The basic matrix operations are addition(+), subtraction(-), multiplication (*), and conjugate transpose(‘) of matrices. In addition to the above basic operations, MATLAB has two forms of matrix division: the left inverse operator \ or the right inverse operator /. Matrices of the same dimension may be subtracted or added. Thus if E and F are entered in MATLAB as

E = [7 2 3; 4 3 6; 8 1 5]; F = [1 4 2; 6 7 5; 1 9 1]; and

G = E - F H = E + F

then, matrices G and H will appear on the screen as G = 6 -2 1 -2 -4 1 7 -8 4 H = 8 6 5 10 10 11 9 10 6

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A scalar (1-by-1 matrix) may be added to or subtracted from a matrix. In this particular case, the scalar is added to or subtracted from all the elements of another matrix. For example, J = H + 1 gives J = 9 7 6 11 11 12 10 11 7

Matrix multiplication is defined provided the inner dimensions of the two operands are the same. Thus, if X is an n-by-m matrix and Y is i-by-j matrix, X*Y is defined provided m is equal to i. Since E and F are 3-by-3 matrices, the product

Q = E*F results as Q = 22 69 27 28 91 29 19 84 26

Any matrix can be multiplied by a scalar. For example, 2*Q gives ans = 44 138 54 56 182 58 38 168 52

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Note that if a variable name and the “=” sign are omitted, a variable name

ans is automatically created. Matrix division can

either be the left division operator \ or the right division operator /. The right division a/b, for instance, is algebraically

equivalent to

while the left division a\b is algebraically equivalent to .

If Z * I = V and Z is non-singular, the left division, Z\V is equivalent to MATLAB expression

I = inv(Z) *V

where

inv is the MATLAB function for obtaining the inverse of a matrix. The right division denoted by V/Z is equivalent to

the MATLAB expression

I = V *inv(Z)

a b

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There are MATLAB functions that can be used to produce special matrices.

Examples are given in Table 1.3.

Table 1.3

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Array operations refer to element-by-element arithmetic operations. Preceding the linear algebraic matrix operations, * / \ ‘ , by a period (.)

indicates an array or element-by-element operation. Thus, the operators .* , .\ , ./, .^ , represent element-by-element multiplication, left division,

right division, and raising to the power, respectively. For addition and subtraction, the array and matrix operations are the same. Thus, + and .+ can be regarded as an array or matrix addition.

If A1 and B1 are matrices of the same dimensions, then A1.*B1 denotes an array whose elements are products of the corresponding elements of A1 and B1.Thus, if A1 = [2 7 6 8 9 10]; B1 = [6 4 3 2 3 4]; then C1 = A1.*B1 results in C1 = 12 28 18

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An array operation for left and right division also involves element-by-element operation. The expressions A1./B1 and A1.\B1 give the quotient of element-by-element division of matrices A1 and B1. The statement

D1 = A1./B1 gives the result D1 =

0.3333 1.7500 2.0000 4.0000 3.0000 2.5000 and the statement E1 = A1.\B1 gives

E1 =

3.0000 0.5714 0.5000 0.2500 0.3333 0.4000

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The array operation of raising to the power is denoted by .^. The general statement will be of the form:

q = r1.^s1

If r1 and s1 are matrices of the same dimensions, then the result q is also a matrix of the same dimensions. For example, if r1 = [ 7 3 5];

s1 = [ 2 4 3]; then

q1 = r1.^s1 gives the result q1 =

49 81 125

One of the operands can be scalar. For example, q2 = r1.^2 q3 = (2).^s1 will give q2 = 49 9 25 and q3 =

4 16 8 Note that when one of the operands is scalar, the resulting matrix will have the same dimensions as the matrix operand.

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MATLAB allows operations involving complex numbers. Complex numbers are entered using function i or j. For example, a number z = 2 + j2

may be entered in MATLAB as

z = 2+2*i or

z = 2+2*j

Also, a complex number za

za = 2 2 exp[( / 4) j]

can be entered in MATLAB as za = 2*sqrt(2)*exp((pi/4)*j)

It should be noted that when complex numbers are entered as matrix elements within brackets, one should avoid any blank spaces. For example,

y = 3 + j4 is represented in MATLAB as

y = 3+4*j

If spaces exist around the + sign, such as

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If w is a complex matrix given as

then we can represent it in MATLAB as w = [1+j 2-2*j; 3+2*j 4+3*j]

which will produce the result w =

1.0000 + 1.0000i 2.0000 - 2.0000i 3.0000 + 2.0000i 4.0000 + 3.0000i

If the entries in a matrix are complex, then the “prime” (‘) operator produces the conjugate transpose. Thus, wp = w' will produce wp = 1.0000 - 1.0000i 3.0000 - 2.0000i 2.0000 + 2.0000i 4.0000 - 3.0000i + + − + = 3 4 2 3 2 2 1 1 j j j j w

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For the unconjugate transpose of a complex matrix, we can use the point transpose (.’) command. For example,

wt = w.' will yield wt =

1.0000 + 1.0000i 3.0000 + 2.0000i 2.0000 - 2.0000i 4.0000 + 3.0000i

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The colon symbol (:) is one of the most important operators in MATLAB. It can be used (1) to create vectors and matrices, (2) to specify sub-matrices and vectors, and (3) to perform iterations. The statement

t1 = 1:6

will generate a row vector containing the numbers from 1 to 6 with unit increment. MATLAB produces the result t1 =

1 2 3 4 5 6

Non-unity, positive or negative increments, may be specified. For example, the statement t2 = 3:-0.5:1 will result in t2 = 3.0000 2.5000 2.0000 1.5000 1.0000 The statement t3 = [(0:2:10);(5:-0.2:4)] will result in a 2-by-4 matrix t3 =

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Other MATLAB functions for generating vectors are linspace and logspace.Linspace generates linearly evenly spaced vectors, while logspace

generates logarithmically evenly spaced vectors. The usage of these functions is of the form: linspace(i_value, f_value, np)

logspace(i_value, f_value, np) where

i_value is the initial value f_value is the final value

np is the total number of elements in the vector.For example, t4 = linspace(2, 6, 8)

will generate the vector t4 = Columns 1 through 7 2.0000 2.5714 3.1429 3.7143 4.2857 4.8571 5.4286 Column 8 6.0000

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Individual elements in a matrix can be referenced with subscripts inside parentheses. For example, t2(4) is the fourth element of vector t2. Also, for matrix t3, t3(2,3) denotes the entry in the second row and third column. Using the colon as one of the subscripts denotes all of the

corresponding row or column. For example, t3(:,4) is the fourth column of matrix t3. Thus, the statement t5 = t3(:,4)

will give t5 = 6.0000 4.4000

Also, the statement t3(2,:) is the second row of matrix t3. That is the statement t6 = t3(2,:)

will result in t6 =

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If the colon exists as the only subscript, such as t3(:), the latter denotes the elements of matrix t3 strung out in a long column vector. Thus, the statement t7 = t3(:) will result in t7 = 0 5.0000 2.0000 4.8000 4.0000 4.6000 6.0000 4.4000 8.0000 4.2000 10.0000 4.0000

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The voltage, v, across a resistance is given as (Ohm’s Law), v = Ri , where i is the current and R the resistance. The power dissipated in resistor R is given by the expression

If R = 10 Ohms and the current is increased from 0 to 10 A with increments of 2A, write a MATLAB program to generate a table of current, voltage and power dissipation.

2

.i

R P=

$"%&'$(

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MATLAB Script

diary ex1_1.dat

% diary causes output to be written into file ex1_1.dat % Voltage and power calculation

R=10; % Resistance value

i=(0:2:10); % Generate current values

v=i.*R; % array multiplication to obtain voltage p=(i.^2)*R; % power calculation

sol=[i v p] % current, voltage and power values are printed diary

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MATLAB produces the following result: sol = Columns 1 through 6 0 2 4 6 8 10 Columns 7 through 12 0 20 40 60 80 100 Columns 13 through 18 0 40 160 360 640 1000

Columns 1 through 6 constitute the current values, columns 7 through 12 are the voltages, and columns 13 through 18 are the power dissipation values.

END POINT FOR THIS PART…

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